Conventionally, in a substrate processing apparatus, there is known an etching processing of selectively etching, between a silicon nitride film (SiN) and a silicon oxide film (SiO2) formed on a substrate, the silicon nitride film by immersing the substrate in a phosphoric acid processing liquid (see Patent Document 1).
In order to etch the silicon nitride film selectively, it is desirable to improve selectivity, which is a ratio of an etching rate of the silicon nitride film with respect to an etching rate of the silicon oxide film, in a latter stage of the etching processing.
Patent Document 1: Japanese Patent Laid-open Publication No. 2013-232593
In the aforementioned substrate processing apparatus, however, since a silicon component is eluted from the substrate as the etching processing progresses, there is a concern that a silicon oxide (SiO2) may be precipitated on the silicon oxide film.